Centrifugal exchangers



A ril 20, 1965 E. CLARIDGE CENTRIFUGAL EXCHANGERS 2 Sheets-Sheet 1 Filed June 13 1961 0 000000000000000 OOOOOOOOOOOOOOOO-T 0000000000000000 0000000000000000 000000 0000000000 OOOOOOOOOOOOOOOO oooooo 00 000000 ANO OOO@ W\MOOOOOOOO H H 4 I O O 0 O O I O 0 0 O O o O a O n O a O nooOooooo O O O O 0 v 0 O O a O I 0 O O O wwy\ :v 4. 4

FIG.

4 3 r 000000000000 000 .6000000000000000 00000000 0000000 O O OOOOOOOOOOO 000000000 0000000 .0000000000000000 J oooooooooooooooo ooomvowoomomvooooo 4 5 4 4 4 FIG. 6

INVENTOR:

ELMOND L. CLARIDGE FIG. 5

HIS ATTORNEY April 1965 E. L. CLARIDGE 3,179,333

CENTRIFUGAL EXGHANGERS Filed June 13, 1961 2 Sheets-Sheet 2 FIG. 2

INVENTOR:

ELMOND L. CLARIDGE BY:M//W% HIS ATTORNEY United States Patent 3,179,333 7 CENTRIFUGAL EXCHANGERS Elmond L. Claridge, Princeton, N.J., assignor to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed June 13, 19 61, Ser. No. 116,769

15 Claims. (Cl. 233-15) The invention relates to improvements in countercurrent flow, centrifugal exchange devices of the type wherein fluids of different densities which are atleast partially immiscible with one another flow in opposed radial directions through perforations in partition walls which surround the axis of rotation of a rotor. The purpose of such countercurrent exchange is to subject one fluid to the solvent action of the other, thereby to wash or extract a constituent or group of constituents. For example, such devices are used in the solvent refining of petroleum fractions and in the purification of chemicals and pharmaceuticals. Usually both fluids are liquid but in some applications the one of lower density may be a gas or vapor.

More particularly, the instant" invention is concerned with an improved construction of the partition walls and a method of controlling internal flow for improving the contacting efliciency.

Known centrifugal countercurrent exchangers comprise a contacting zone formed by a series of radially spaced, perforated partition walls which surround the axis of rotation substantially concentrically, i.e., which are concentric cylinders or which form a continuous spiral, the turns of which are so closely spaced as to function practically as cylinders. These walls are encased in a cylindrical rotor casing mounted on a hollow shaft extending beyond both ends of the casing. The shaft contains at least four channels, e.g., provided by two axial pipes mounted within bores in the two ends of the shaft and each defining an inner channel and an outer annular channel, connected by separate radial passageways to different regions of the rotor, so that fresh denser fluid is supplied to a radially inner part of the extraction zone near to but usually not immediately next to the shaft, fresh other fluid is supplied to a radially outer part of the extraction zone, the contacted denser liquid is withdrawn from the radially outer part of the rotor, usually immediately adjacent to the rotor housing, and the other contacted liquid is discharged from the radially inner part of the rotor, usually immediately adjacent to the shaft. Bearings, bearing support, seal rings, and chambers surrounding the shaft are provided at both ends of the shaft for the separate discharge and supply of the fluids and means are provided at one end of the shaft for applying a torque to cause rotation. The perforated concentric partition walls are normally maintained with a radial spacing, typically about 0.2 to 3 inches, by the use of suitable spacers or indentations (dimples) at regular intervals over their surfaces. The entire device may be encased in a protective stationary shell.

In operation, the fluids to be extracted and the extraction solvent are introduced by pumps, usually via heat exchangers and flow-control devices, While the rotor is rotated at an appropriate speed, usually in the range of 500 to 5060 rpm. The centrifugal forces developed in the rotor far exceed the force of gravity, so that the latter force has a negligible influence on the manner of flow of the fluids inside the rotor. The apparatus, therefore, acts in a manner analogous to a gravity-flow perforated plate extraction column; the region near the shaft corresponds to the top of such a column and the region at the periphery to the column bottom. Major points of dissimilarity are that centrifugal force is substituted for gravitational force and the area of the plates increases toward the periphery.

3,179,333 Patented Apr. 20, 1965 The relative proportions of the fluid phases within the rotor are adjusted by controlling the back pressure on the low-density exit stream. Usually this leads to a preponderance of one phase in a given space or compartment between adjacent perforated partition walls and the preponderant phase is usually continuous, i.e., it will surround droplets of'the other phase as the latter flows through the holes into the said space. Ideally, these droplets travel across the space in their settling direction (radially outwards if they are the denser fluid and radially inwards if the fluid of lower density) and may form a thin layer of coalesced fluid against the next wall before flowing through the holes therein for dispersal within the next inter-wall space. Also ideally, the continuous phase moves from one inter-wall space to the next without being dispersed and coalesced, in a direction opposite to that of theudispersed phase and thence through holes in the next wa It was found in practice that the exchange between the phases or, stated otherwise, the contacting efiiciency attained, is often far below that expected from the known overall flow rates and properties of the fluids. In an effort to determine the causes of such low efficiences radioactive tracer tests were performed in a commercial centrifugal extractor of the type described above. These tests indicated the occurrence of very high entrainment of extractor having partition walls which are shaped to reduce the entrainment of a phase by another.

Still additional objects will become apparent from the following description.

In summary, according to the invention internal entrainment is reduced by providing two sets of holes, each hole having lips which project from the partition walls in the radial downstream directions of the respective phases flowing therethrough partly to the next partition and locating the passages thus formed in an interspersed array so that each discharges its fluid toward an imperforate region of the next wall. The inlet ends of such passages are substantially flush with the sides of the partition walls opposite to the said lips. Preferably the lips extend downstream for distances between 0.2 and 0.5 of the radial interwall space. Within any one partition wall or major segment thereof (i.e., subtending an are between 180 and 360, whether cylindrical or spiral) the sizes of the set of passages for the disperse fluids are preferably uniform, but in most instances different from, and usually less than, the dimensions of the passages of the other set. The latter are preferably also of uniform size within the extend of the wall although this is not in every case essential. It is thereby possible to design the sizes so as to attain a highly desirable physical condition, namely, that the pressure drops through the several passages balances the hydrostatic forces at or only slightly above, i.e., not over above, the non-em training internal flow rates when the contactor is operated at design external flow rates. This design of the orifice sizes will become clear from the following explanation.

Because a basic understanding of the hydrostatic forces,

flows and pressure balances prevailing in such centrifugal apparatus is essential for an undestanding of the invention the detailed description will be preceded by a consideration thereof.

In the centrifugal extractor, as in a gravity-flow perforated plate column, the relative proportions of the two phases can be adjusted by controlling the pressure balance between the two exit streams; usually the preponderant phase is continuous, and droplets of the other phase are dispersed in the continuous phase upon passage through the holes and travel across the contacting space more or less radially between the partition walls. Upon reaching the next wall, partial or complete coalescence usually occurs, with the formation of a thin layer of the previously dispersed phase before flowing through the holes in the next plate. The continuous phase moves without significant dispersion in the opposite radial direction and then flows thence through holes in the next wall which are generally different from those traversed by the dispersed phase. The driving forces for this countercurrent flow are the buoyant force on the droplets due to the centrifugal field and the pressure drop through the entire apparatus for the continuous phase.

Viscous drag forces account for localized or partial deviations from the general flow of the continuous and dispersed phases through the apparatus. For example, a thick film of the continuous phase is dragged along by the dispersed droplets as they move in their settling direction; and the mass movement of the continuous phase exerts a retarding effect on the motion of droplets in the other direction. Where local velocities of the continuous phase are high, as in flowing through perforations, the net direction of motion of droplets of the dispersed phase is often in the same direction as the continuous phase. In other words, droplets of the dispersed phase are entrained and move in a direction opposite to their settling direction; this is sometimes called backmixing. Any such entrained phase must be separated from the continuous phase in some manner for eventual return flow in the disperse phase settling direction or else it will eventually leave the apparatus in the continuous phase exit stream. Likewise, with regard to droplets moving in their settling direction, in regions of the contacting space wherein they are not duly impeded by the continuous phase mass movement, as they approach the next wall, they get within such close proximity to one another that their viscous envelopes of continuous phase offer great resistance to the counterflow of continuous phase in the interval between the drops. Collecting of drops into a continuous film is therefore slower than their free settling rate. If the time available for collection of the drops into a continuous layer at the next partition wall, as a consequence of the balance between buoyant forces and frictional resistance to flow through the orifices, is less than the time required for the coalescing process to be complete, then a mixture of droplets and continuous phase will flow through some of the holes in the main flow direction of the dispersed phase. This constitutes entrainment of the continuous phase in the wrong direction. Again, this continuous phase must be separated in some region and returned in the proper flow direction or else leave the apparatus as entrainment in the contacted dispersed phase.

It is generally possible to design and operate an apparatus of the type described without entrainment in the exit streams by providing more phase separating capac ity near the discharge region than is provided in the intermediate contacting regions between the several partition walls, and by operating at flow rates exceeding the settling capacity of the intermediate regions, but within the settling capacity of the discharge regions, whereby a high degree of internal entrainment of one or both phases occurs.

It was found according to the invention that the sizes and configurations of the holes have a considerable effect on this tendency toward entrainment. If the hole area used by the dispersed phase is low enough to cause considerable frictional resistance to the flow of the dispersed phase which is collected and coalesced as a film on the upstream side of the wall, this film will build up to an appreciable thickness. The centrifugal buoyant force exerted on this relatively thick layer of coalesced phase is thus used to force the required flow of this phase through the hole. If, on the other hand, the hole area is large, the frictional resistance is low and the buoyant force will move entrained continuous phase as well as disperse phase through the holes.

The magnitude of this effect of hole area on entrainment is governed by the pressure balance around a circuit comprising two contacting spaces and the holes in the intervening partition wall used by the counter-flowing streams. If the buoyant force due to different phase ratios (and, hence, different densities) in the two counterflowing streams is equated to the sum of the frictional pressure drops encountered by the two counter-flowing streams (these frictional pressure drops increasing with the flow rates of the streams and being further influenced by the sizes and shapes of the holes), a hydraulic balance is established at flow rates suflicient to satisfy the equation. Should these flow rates exceed the non-entrained flow rates (which can be calculated from the external flow rates or charge rates, and the physico-chemical properties of the fluids), then entrainment must occur. If the average phase ratio or the ratio in either stream is known, the effect of this extent of entrainment in reducing the extraction efliciency can also be calculated.

It is not practicable to obtain samples of the flowing phases between intermediate contacting spaces within an operating centrifugal exchanger. However, radioactive tracer tests were made on such an apparatus used for extracting lubricating oil with phenol as a selective Solvent. These tests showed entrainment in both directions to be at least four to five times the non-entrained flow rates, and the contacting efiiciencies for the annular contacting spaces were estimated to be reduced from about or higher to about 78%. It is evident that there is room for a significant improvement in contacting efficiencies which are unduly low because of entrainment, which was not heretofore recognized to play such a significant role in apparatus of this type.

In accordance with the invention, entrainment is reduced by the following expedients, it being understood that the invention is not restricted to the simultaneous practice of all:

(1) The pressure drop through the perforated partition walls should be such as to establish a hydraulic balance at or moderately above, i.e., not over above, the non-entrained interal flow rates for the external flow rates at design values. The allowance of moderate entrainment is usually necessary in order to allow for variations in desired internal flow rates as operating conditions are changed or feed stocks of different physico-chemical properties are processed.

(2) Most of the frictional pressure drop thus provided should occur in flow of the collected disperse phase through the holes in the partition walls, in order (a) To ensure that a layer of collected disperse phase is maintained on the upstream of entrance ends of the holes through which this phase flows, and

(b) To avoid the necessity of using a low hole area for the flow of the continuous phase in the opposite direction. If the latter phase were made to flow through a small hole area there would result the undesirable effects of (1) causing a local high velocity of the continuous phase in the region of the holes through which it flows, which could lead to entrainment of the disperse phase in the continuous phase flow, and (2) increasing the pressure drop for flow of continuous phase through the extractor, thereby requiring high pressure from the feed pump to cause the desired rate of flow of continuous phase.

(3) Means must be provided to direct the flow of collected disperse phase through only selected holes and the flow of continuous phase only through other holes in the partition wall.

(4) The number of holes for flow of disperse phase should be approximately equal to and appropriately spaced with respect to the holes for the continuous phase, so as to maximize contact between the phases and to minimize by-passing. In a preferred arrangement the perforations are arranged so that, except at the margins of the walls, each perforation for the flow of disperse phase has a pair of perforations for the'continuous phase situated respectively at opposites thereof.

In order to allow for the interaction between rotational motion of the rotor and movement of the phases parallel to the walls, each phase entering a contacting space should be able to travel at an angle to the axis of the rotor as it flows parallel to the surfaces of the Walls, pass by a stream of the other phase, and then within a limited range of distance be able to reach the perforations by which it may leave the contacting space. Desirably, the distance between the entry and exit of a phase to and from a contacting space is not less than about three nor more than about twenty times the radial thickness of the contacting space. By these arrangements tendencies toward excessive vibration are reduced. Mechanical imbalance of the rotor and its contents, tending to cause vibration, may be caused by inappropriate distribution of perforations such that large accumulations of one phase or the other occur in some regions of the contacting spaces.

Having indicated the nature of the invention; reference is made to the accompanying drawing forming a part of this specification and showing certain preferred embodiments, wherein:

FIGURE 1 is a diagrammatic perspective view of the centrifugal exchange device, parts being broken away and stationary parts being shown in dashed lines;

FIGURE 2 is an axial sectional View through the rotor;

FIGURE 3 is a plan view of part of one of the perforated partition walls prior to being bent into cylindrical shape;

FIGURE 4 is a perspective view of parts of three partition walls showing the relation between their-perforations;

FIGURE 5 is an enlarged detail view of a portion of FIGURE 4; and

FIGURES 6 and 7 are views corresponding to FIG- URE 3 but showing alternative arrangements of the holes.

Referring to the drawings, and particularly to FIG- URES l and 2, the contactor comprises a supporting framework 11 which carries a rotatable shaft 12 upon which is mounted a rotor 13. As shown in dotted lines in FIGURE 1, the rotor is provided with a stationary casing comprising upper and lower sections 14 and 15. Torque for driving the rotor is applied to a drive pulley 16. The shaft 12 has two axial boreswhich are interrupted at the rotor and contain smaller coaxial pipes 17 and 18, respectively, to define four channels: A pair of supply channels within the pipes 17 and 18 for the influx to the rotor of the heavier and lighter fluid, respectively, and annular channels 19 and 2th for the efllux of contacted lighter and heavier fluids, respectively. The inlet ends of the pipes 17 and 18 communicate through bores in stationary caps 21 and 22 at the extremities of the shaft with inlet openings 23 and 24, respectively, suitable sealing means being provided at 25 and 26 to isolate the infiowing fluids from the outflowing fluids. Outlet pipes 27 and 28 communicate with the annular channels 19 and 20, respectively.

The rotor 13 comprises a hub 9, which is fixed to the shaft, a rotor housing which includes a pair of annular end plates 29 and 30 fixed to the hub, and a peripheral wall 31 to define a closed chamber. Within the rotor and spaced from the end plates with a small clearance sufllcient to provide flow spaces adjacent the plates 29 and 30 are interior annular end plates 32 and 33 which are joined to the hub and terminate radially short of the wall 31. A plurality of concentric perforated partition walls 34 is mounted in radially spaced relation between the interior end plates to define a plurality of annular contacting spaces or compartments of progressively increasing radii. The radial dimensions of such spaces are typically between 0.2 and 3 inches. Fresh heavier fluid from the pipe 17 is admitted to a contacting compartment at a radially inner part of the rotor but preferably not the innermost compartment by one or more radial tubes 35 and passages 36 formed in the shaft. These tubes extend through holes in the inner partition walls with close fits. Contacted lighter fluid flows from the space immediately surrounding the hub 9 into the annular channel 19 via one or more ports 37 formed in the hub 9 and shaft 12. Fresh lighter fluid from the pipe 18 is admitted to a contacting compartment at a radially outer part of the rotor, but preferably not to the outermost compartment, by one or more tubes 38 and passages 39 drilled in the end plate 33. Contacted heavier fluid flows from the space immediately adjoining the peripheral wall 31 through a radial passage 40 between the end plates 29 and 32 and also through a radial passage 40a between the end plates 39 and 33, and thence via registering ports in the hub 9 into passages 41 and 41a formed in the shaft. Flow from the passage 40 is further through an axial passage 42 milled into the hub. Vancs 43 extending generally radially and either straight or curved as shown like turbine blades may be provided within the passages 49, and 40a to aid in reducing the circumferential velocity of the fluid which moves radially inward.

The el ments described up to this point, except the perforated walls 34, are known per se and commercially available and are, therefore, not further described.

Considering now the invention, each of the partition walls 34 is provided with two sets of holes 44 and 45, respectively, preferably equal in number and generally equal in size within each set but unequal in size between the sets for a flow of the denser and less dense fluid, respectively, and provided with peripheral lips, e.g., shaped as craters, extending in the discharge directions from about 0.2 to 0.5 of the radial interval between adjacent partition walls. In the example shown these are formed by deforming the periphery of flat holes in a sheet metal plate which is to form the partition wall with a suitable pressing tool, in such a way that the entrances to the holes lie flush with the partition walls but the periphery of the hole is raised or depressed; however, the invention is not restricted to any specific mode of forming such lips nor to the exact contours illustrated. Also, while the holes of the set 44 are shown to be larger than those of the set 45, this is not restrictive of the invention, and in other instances the holes for the radially inward flow of the lighter fluid would be larger. The hole dimensions are further described below.

FIGURE 3 shows one perforated plate prior to being rolled to form a partition wall; the holes of the two sets are arranged in alternate rows parallel to the long edge, i.e., to lie circumferential to the rotor axis when assembled, as is shown in FIGURE 2. However, the rows can extend in other directions, such as parallel to the shorter edge as shown in FIGURE 6, or at an angle to the edges as shown in FIGURE 7. The orientations of FIGURES 3, 6. and 7 represent only three of various possible arrangements.

The several walls can be arranged within the rotor in the relation shown in FIGURE 4, wherein portions of three contiguous walls 34a, 34-]: and 34c appear. The row of holes of one set lie in the same radial plane as the row of holes of the other set in the next adjacent wall, but the holes in contiguous walls are displaced in the circumferential direction in order to conform to the requirements in the next paragraph below. To maintain these relations throughout the rotor it is, of course, necessary to provide the same number of holes in all partition walls and to vary the circumferential spacing between holes in successive walls.

FIGURE 5 shows the shapes of the lips and the relation of the holes on the three walls 34a, 34b and 34c.

It will be noted that each hole is situated opposite an imperforate region of the contiguous plate, and that the distance from each hole of a given set in one wall to the nearest hole of the same set in the contiguous wall is between about three and twenty times the interval between the walls.

When the rows of holes are oriented obliquely, as is shown in FIGURE 7, the rows become helical when the plates are rolled to form the partition walls. It is possible to vary the spacings of the rows and to assemble the plates so that each hole of one set will lie between holes of the other set on the contiguous plates. Alternatively, the consecutive walls may have the rows disposed in opposite directions, so that the resulting helical rows are clockwise in one wall and counterclockwise on the next.

Regardless of what specific arrangement of hole locations is used, it is important to avoid having holes of the same set in consecutive partition walls situated opposite one another, i.e., on the radius, because this would lead to by-passing. By the arrangements described above each phase must cross the path of the opposite phase within each contacting space before reaching the hole in the next wall.

The particular size relation illustrated, wherein the .holes 44 are larger, is suitable for the case in which the lower-density phase has a lower flow rate than the other; usually, in such a situation the lower-density phase is dispersed in the other phase. The size relationship is reversed when the lower-density phase predominates and becomes the continuous phase.

The diameters of the larger as well as of the smaller holes should preferably be maintained constant over the area of each partition wall. However, the diameters of the holes should, for optimum results, be different in successive partitions (in practice, they may be the same in a limited number of consecutive walls) in accordance with the radial distance from the axis of rotation. The hole diameters are chosen as follows:

The diameter of the holes assigned to the disperse phase varies directly as the square root of the desired internal flow rate of that phase at any cylinder radius, directly as the fourth root of the density of that phase at said cylinder radius, inversely as the square root of the angular rotational speed of the rotor, inversely as the fourth root of the cylinder radius, and inversely as the fourth root of the difference in density of the two phases at the said cylinder radius. Since the angular rotation is constant for all radii, and the number of holes can be made the same in all partition walls, as was explained above, and because the density and density difference often do not vary widely (so that their fourth roots will vary very little) with changing radii, the hole diameter will vary principally as the square root of the desired internal flow rate divided by the fourth root of the radius.

The desired internal flow rate of the dispersed phase as a function of radius can be calculated from the external flow rates, the mutual solubility, and an estimate of the ideal stage number as a function of the radius. From these the compositions and amounts of the phases flowing between contacting spaces at any radius can be determined by known physico-chemical procedures, as is well known in the solvent extraction art.

The variation in hole size for the dispersed phase with cylinder radius is thus determined, but the hole size at a given radius has not yet been specified. The general formula for nominal hole diameter for the disperse-phase hole is:

wherein D =hole diameter, inches Q=flow rate of disperse phase, cubic inches per minute d =density of disperse phase, pounds per cubic foot C =orifice coefiicient, dimensionless n=number of disperse-phase holes N :rotational speed in revolutions per minute R =radius of cylinder, inches Ad=difference in density between continuous and dispersed phases, pounds per cubic foot h=head due to disperse phase buoyancy in the region of the disperse phase holes, inches of collected disperse phase measured from the exit of the holes The quantity It should not exceed twice the height of the crater-shaped lip projecting from each hole. In operation, the rotor speed N will usually be varied to arrive at optimum operation, egg, in extracting petroleum oils as diiferent feed stocks are processed or throughput and operating conditions are varied. Thus, the rotor should be designed for the average feed stock, throughput and operating conditions, and for mean rotor speed of the efiective range of rotor speeds. The number of holes and the diameters are adjusted to result in a reasonable range of hole diameters over the range of cylinder radii, Typically, R has a range of 9 to 30 inches. Q, d and Ad are determined from the external feed rates and equilibrium compositions which are computed from mutual solubility data, as was mentioned previously.

In solvent extraction of petroleum fractions such as lubricating oils or cycle oils, Q varies from about 0.8-1.0 times the external oil charge rate at the dense phase (solvent) inlet to about 1.5-2.0 times the external oil charge rate in the region of the light phase (oil) inlet, while the ratio Ad/d varies from about 0.1-0.2 at the dense phase inlet to a value approximately /3 to as great at the light phase inlet. For this type of variation of Q and Ad/d with radius, the hole diameter D will remain approximately constant over the range of R or may increase by a factor of about 1.1-1.25 as R increases from the region of the dense phase inlet to the region of the light phase inlet. In systems where the extract yield may be low (5-1 0% or less) and the mutual solubility of the two phases is relatively slight, Q and Ad/d will vary only slightly over the range of R. The hole diameter D will then vary primarily as the inverse fourth root of the radius R. In the region between the light phase inlet and the outer periphery of the rotor, Q may vary from 0.0 to about 1.0 times the external charge rate of light phase. In general, for this region the value of D should be calculated on the basis of Q=1.0 times the external light phase charge rate. Alternatively, since this region and that lying between the dense phase inlet and the hub are primarily final settling regions and do not aifect appreciably the extraction efiiciency of the apparatus, any other designs already known and proven effective may be used for the cylindrical walls in these end sections.

The actual hole diameters for the disperse phase holes should be made somewhat, e.g., 20 to 40%, larger than the nominal diameters determined by the above equation. The reason for this is that the formula is based on the assumption that the disperse phase is entirely settled, whereas in actuality some dispersed phase is continually in transit through the continuous phase within each contacting space. This diminishes the thickness of the layer of collected disperse phase, but the buoyant force tending to cause flow through the disperse phase holes is not appreciably dirninishedthereby. Disperse phase must be continually coalescing at the collected disperse phase-continuous phase interface. The last stages of this coalescing process are often slow in relation to the settling rate of the disperse phase; hence it may be necessary to tolerate a minor amount of entrainment of continuous phase in the disperse phase stream flowing through the holes. Additional flow capacity is, therefore, needed in these holes.

Furthermore, the formula given above is based on utilization of the full buoyant force to overcome the pressure drop in the holes used for the disperse-phase flow. For hydraulic balance, however, the pressure drop for 9 flow of continuous phase through the continuous-phase holes must be included in the total pressure drop balanced by the buoyant force. The effective driving force for flow of disperse phase through its holes is, therefore, reduced and the hole diameters must be increased to compensate for this. If the actual disperse-phase hole diameter is made about 1.3 times the nominal hole diameter, the area will be 1.7 times as great, while the pressure drop will be diminished by a factor of 1.3 or 2.85, at the non-entrained flow rate of the disperse phase. Maximum entrainment will in such a case be about 70% of the nonentrained flow rate; this compares favorably with the minimum of 400% to 500% entrainment found by the abovementioned tests to occur with prior designs. Further, pressure drop is sufliciently reduced to allow a facile establishment of hydraulic balance with a reasonable hole size for continuous phase.

The hole sizes for the continuous phase may be determined by multiplying the hole area for the disperse phase by twice the ratio of the flow rates of the continuous phase to the dispersed phase.

In determining the relative numbers and diameters of holes, attention should be paid not only to maintaining a reasonable minimum size for the smallest holes but also to the spacing requirement mentioned earlier.

Aside from the essentially different design of the hole shapes and the selection of their diameters and location, the apparatus may be constructed in accordance with existing designs.

I claim as my invention:

1. In centrifugal apparatus for countercurrent exchange of at least partially immiscible fluids of different densities, the combination of: a rotor having an axial shaft mounted for rotation, a plurality of radially closely spaced partition walls within said rotor and surrounding said shaft substantially concentrically, means for supplying the denser fluid to and discharging the other fluid from the rotor interior at radially inner portions thereof, and means for discharging the denser fluid from and supplying the other fluid to the rotor interior at radially outer portions thereof, said partition walls having two sets of small holes distributed in repetitively interspersed relation both along the circumferential and axial directions within each partition wall for the predominantly separate flow of said fluids through the holes of the respective sets each of said holes being situated opposite to an imperforate area in the respectively adjacent partition walls, the holes of one set having peripheral lips extending partly to the next radially outer partion wall and defining passages for the flow of said denser fluid and having their inlets substantially flush with the radially inner surfaces of their respective partition walls, and the holes of the other set having peripheral lips extending partly to the next radially inner partition wall and defining passages for the flow of said other fluid and having their inlets substantially flush with the radially outer surfaces of their respective partition walls, the distance between each hole in any partition wall and the nearest holes of the same set in the same partition wall being greater than the radial interval between said partition wall and the next partition wall toward which the lips of said holes are directed 2. Apparatus as defined in claim 1 wherein said peripheral lips extend toward their respective partition adjacent wall through distances between 0.2 and 0.5 of the radial distance between adjacent partition walls.

3. Apparatus as defined in claim 1 wherein the distance between each hole in one partion wall and the nearest hole in the next adjacent partition wall having a lip directed in the same radial direction is between about three and twenty times the radial interval between said parti- 5. Apparatus as defined in claim 4 wherein the areas of the passages of said other set are also alike throughout the said partition wall.

6. Aparatus as defined in claim 1 wherein the numbers of holes is the same in each set, the holes of the said sets being regularly spaced both about the circumference and in the direction parallel to the axis of the shaft so that, except at the margins of the walls, each hole of the first set has a pair of holes of the other set situated respectively at opposite sides thereof.

7. In centrifugal apparatus for countercurrent exchange of at least partially immiscible liquids of different densities, the combination of: a rotor having an axial shaft mounted for rotation, a plurality of radially closely spaced partition walls within said rotor and surounding said shaft substantially concentrically, means for supplying the denser liquid to and discharging the other liquid from the rotor interior at radially inner portions thereof, and means for discharging the denser liquid from and supplying the other liquid to the said rotor interior at radially outer portions thereof, said partition walls having two sets of holes distributed in repetitively interspersed relation both along the circumferential and axial directions within each partition wall for the predominantly separate flow of said liquids through the holes of the respective sets, the holes of each set having, in each partition wall, like areas which are different from those of the other set, each of said holes being situated opposite to an imperforate area in the respectively adjacent partion Walls, said holes having peripheral lips at their discharge ends which define passages extending toward adjacent partition walls for distances between 0.2 and 0.5 of the radial distance between adjacent partition walls and being flush with the surfaces of the partition walls at their entrance ends, the iips of the set of holes for flow of the denser liquid being directed radially outwards and the lips of the other set for the flow of the other liquid being directly radially inwards.

8. In centrifugal apparatus for countercurrent exchange of at least partially immiscible liquids of different densities, the combination of: a rotor having an axial shaft mounted for rotation, a plurality of radially closely spaced partition walls within said rotor and surounding said shaft substantially concentrically, means for supplying the denser liquid to and discharging the other liquid from the rotor interior at radially inner portions thereof, and means for discharging the denser liquid from and supplying the other liquid to said rotor interior at radially outer-portions thereof, said partitions having two sets of holes distributed in repetitively interspersed relation within each partition wall for the predominantly separate flow of said liquids through the holes of the respective sets, one of said liquids forming a disperse phase and the other a continuous phase within each space between partition walls, the holes of each set, within each partition wall, having like areas which are different from those of the other set, each of said holes being situated opposite to an imperforate area in the respectively adjacent partition walls, said holes having peripheral lips at their discharge ends which define passages extending toward adjacent partition walls for distances which are minor in relation to the radial distance between adjacent partition walls and being flush with the surfaces of the partition walls at their entrance ends, the lips of the set of holes for the flow of denser liquid being directed radially outwards and the lips of the other set for the flow of the other liquid being directed radially inwards, the sizes of the holes of the set for the flow of the disperse liquid phase being progressively smaller at increasing radii of the partition walls.

9. Apparatus as defined in claim 8 wherein the diameters of said holes for the flow of the disperse liquid phase vary substantially inversely as the fourth root of the radius from the rotor axis to the partition wall.

10. Apparatus as defined in claim 9 wherein the diameters of the holes for the flow of the continuous liquid phase also vary substantially inversely as the fourth root of the radius.

11. In centrifugal apparatus for the countercurrentexchange of at least partially immiscible fluids of different densities, the combination of: a rotor having an axial shaft mounted for rotation, a plurality of radially closely spaced partition Walls within said rotor and surrounding said shaft substantially concentrically, means for supplying the denser fluid to and discharging the other fluid from the rotor interior at radially inner portions thereof, and means for discharging the denser fluid from and supplying the other fluid to the rotor interior at radially outer portions thereof, said partition walls having two sets of small holes distributed in repetitively interspersed relation within each partition wall, means for effecting predominantly separate flows of said fluid through the respective sets of holes in opposite directions, each of said holes being situated opposite to an imperforate area in the respectively adjacent partition walls, the holes of at least one set, within each partition wall, having like areas which are different from those of the other set, the diameters of the holes of said one set, within each partition wall, having like areas which are different from those of the other set, the diameters of the holes of said one set being substantially inversely proportional to the fourth root of the radius from the rotor axis to the partition wall.

12. Apparatus as defined in claim 11 wherein the diameters of the holes of the other set also vary substantially as the fourth root of the radius.

13. In centrifugal apparatus for the countercurrent exchange of at least partially immiscible liquids of different densities, the combination of: a rotor having an axial shaft mounted for rotation, a plurality of radially closely spaced partition walls within said rotor and surrounding said shaft substantially concentrically, means for supplying the denser liquid to and discharging the other liquid from the rotor interior at radially inner portions thereof, and means for discharging the denser liquid from and supplying the other liquid to the rotor interior at radially outer portions thereof, said partition walls having two sets of small holes distributed in repetitively dispersed relation within each partition wall, means for effecting predominantly separate flows of said liquids through the respective sets of holes in opposite directions, one of said liquids forming a disperse phase and the other a continuous phase between partition walls and a layer of the disperse phase forming a layer thereof against each wall, each of said holes being situated opposite to an imperforate area in the respectively adjacent partition walls, the holes of the set for the flow of the disperse liquid, within any one partition wall, having like areas which are less than the areas of the holes for the flow of the continuous liquid, said disperse liquid holes having difierent diameters in successive partition walls, said diameters, in inches, being between LOD and 1.4D, wherein D is equal to Q is the flow rate of the disperse liquid through the Wall in cubic inches per minute,

d is the density of the disperse liquid in pounds per cubic foot,

C is the orifice coefficient of the holes,

n is the number of disperse-phase holes through the wall,

N is the rotational speed of the rotor in revolutions per minute,

R is the radius of the partition wall from the rotor axis in inches,

Ad is the'dilference in density between the continuous and dispersed liquids at the entrance side of the holes 'in pounds per cubic foot, and

h is the head due to disperse phase buoyancy at the entrance to the hole, in inches.

14. Apparatus as defined in claim 13 wherein said means for effecting predominantly separate flows of liquids are peripheral lips which surround the holes and extend partly toward the next partition wall in the downstream direction for the liquid flowing through the respective hole. i

15. Method of contacting two at least partially immiscible liquids countercurrently within a rotor which contains a series of annular contacting stages situated at different radii from the rotor axis and separated by partition closely spaced walls each having two sets of repetitively distributed holes therein, which comprises the steps of: rotating said rotor about its axis to establish a centrifugal field, supplying the liquids of greater and lesser densities to the rotor interior respectively at radially inner and radially outer regions thereof, discharging the contacted liquids of greater and lesser densities from the rotor interior respectively at radially outer and radially inner regions thereof, flowing one of said liquids as continuous phase progressively through said contacting stages by passage through one set of said holes in the successive walls against an imperforate region of the adjacent wall, flowing the other liquid as disperse liquid progressively through said contacting stages in a radial direction opposite to the flow of the continuous liquid by flowing the disperse liquid through the other set of holes against an imperforate region of the adjacent wall, dispersing the disperse liquid within the continuous liquid, and collecting a thin layer of the disperse liquid on the wall at the downstream side of each stage before flow through the holes therein, and restricting recirculation of liquid between stages by flowing the disperse liquid through the partition walls as small streams having, at any partition wall, like diameters which are smaller than the streams of the con-tinuous phase flowing in the opposite direction, said like diameters, in inches, being between 1.0 and 1.4 of the value wherein Q is the flow rate of the disperse liquid through the wall in cubic inches per mintue,

d is the density of the disperse liquid in pounds per cubic foot,

C is the orifice coefficient of the holes,

n is the number of disperse-phase streams flowing through a wall,

N is the rotational speed of the rotor in revolutions per minute,

R is the radius of the partition wall from the rotor axis in inches,

Ad is the differences in density between the continuous and dispersed liquids in the stage at the upstream ends of the disperse liquid streams in pounds per cubic foot, and

h is the head due to disperse phase buoyancy in the stage: at the upstream ends of the disperse liquid streams, in inches.

References flited by the Examiner UNITED STATES PATENTS 622,393 4/99 Reid d 233-43 2,281,616 5/42 Plocek 26183 2,286,157 6/42 Podbielniak 233l5 2,291,849 8/42 Tomlinson 233l5 2,670,132 2/54 Podbielniak 233l5 2,758,783 8/56 Podbielniak 233-15 2,758,874 8/56 Podbielniak et al 23315 FOREIGN PATENTS 233,878 5/25 Great Britain.

HARRY B. THORNTON, Primary Examiner.

HERBERT L. MARTIN, Examiner. 

1. IN CENTRIFUGAL APPARATUS FOR COUNTERCURRENT EXCHANGE OF AT LEAST PARTIALLY IMMISCIBLE FLUIDS OF DIFFERENT DENSITIES, THE COMBINATION OF: A ROTOR HAVING AN AXIAL SHAFT MOUNTED FOR ROTATION, A PLURALITY OF RADIALLY CLOSELY SPACED PARTITION WALLS WITHIN SAID ROTOR AND SURROUNDING SAID SHAFT SUBSTANTIALLY CONCENTRICALLY, MEANS FOR SUPPLYING THE DENSER FLUID TO AND DISCHARGING THE OTHER FLUID FROM THE ROTOR INTERIOR AT RADIALLY INNER PORTIONS THEREOF, AND MEANS FOR DISCHARGING THE DENSER FLUID FROM AND SUPPLYING THE OTHER FLUID TO THE ROTOR INTERIOR AT RADIALLY OUTER PORTIONS THEREOF, SAID PARTITION WALLS HAVING TWO SETS OF SMALL HOLES DISTRIBUTED IN REPETITIVELY INTERSPERSED RELATION BOTH ALONG THE CIRCUMFERENTIAL AND AXIAL DIRECTIONS WITHIN EACH PARTITION WALL FOR THE PREDOMINANTLY SEPARATE FLOW OF SAID FLUIDS THROUGH THE HOLES OF THE RESPECTIVE SETS EACH OF SAID HOLES BEING SITUATED OPPOSITE TO AN IMPERFORATE AREA IN THE RESPECTIVELY ADJACENT PARTITION WALLS, THE HOLES OF ONE SET HAVING PERIPHERAL LIPS EXTENDING PARTLY TO THE NEXT RADIALLY OUTER PARTION WALL AND DEFINING PASSAGES FOR THE FLOW OF SAID DENSER FLUID AND HAVING THEIR INLETS SUBSTANTIALLY FLUSH WITH THE RADIALLY INNER SURFACE OF THEIR RESPECTIVE PARTITION WALLS, AND THE HOLES OF THE OTHER SET HAVING PERIPHERAL LIPS EXTENDING PARTLY TO THE NEXT RADIALLY INNER PARTITION WALL AND DEFINING PASSAGES FOR THE FLOW OF SAID OTHER FLUID AND HAVING THEIR INLETS SUBSTANTIALLY FLUSH WITH THE RADIALLY OUTER SURFACES OF THEIR RESPECTIVE PARTITION WALLS, THE DISTANCE BETWEEN EACH HOLE IN ANY PARTITION WALL AND NEAREST HOLES OF THE SAME SET IN THE SAME PARTITION WALL BEING GREATER THAN THE RADIAL INTERVAL BETWEEN SAID PARTITION WALL AND THE NEXT PARTITION WALL TOWARD WHICH THE LIPS OF SAID HOLES ARE DIRECTED. 